1QwkSport2.5r

Well gee guys... nobody can do a google search to find information that Mecoa has posted right on their website? I know there’s a zillion iterations of the K&B .40 engine that’s had a half dozen different carburetors over the years. All you need is a wide enough adjustment for the thing to run. Again, not rocket science guys. Most of the K&B .40s made over the last 20-25 years uses a mixture disc for the idle - this is on an eccentric screw that rotates only a little bit in either direction of center. Start in the center on this. Usually very little adjustment is needed to the idle mixture unless you’re using real low nitro or real high nitro fuel.

K&B .40 ABC Marine #4075 - 3-1/2 turns for the main needle. http://www.mecoa.com/kb/40/4075.htm
K&B .40 Ringed Marine #4012 - 2-1/2 turns for the main needle. http://www.mecoa.com/kb/40/4011.htm

As long as the needle valve is open enough for the engine to run, a competent tuner should be able to figure out if it’s rich, lean, or just right.

1QwkSport2.5r

I know several people that know a thing or two about old engines. If I don’t know something, and my pals don’t either, I google. Not real hard to do.

1967brutus

I'd say...

If a click or two towards richer does not improve things, chances are it was allready too rich to begin with, and the opposite is true for a few clicks leaner.

Indeed no rocketscience...

1QwkSport2.5r

Pretty quiet now. Interesting...